It is proposed to determine whether certain common air pollutants, such as excited singlet molecular oxygen, be involved in the oxidation of membrane-bound cholesterol in select biological membranes and in model systems. Analysis of the cholesterol hydroperoxides initially formed in such systems upon exposure to the air pollutants can be used to determine whether excited singlet molecular oxygen or ground-state triplet oxygen be involved. The sterol hydroperoxides will be analyzed by means of thin-layer and gas chromatographic methods already developed and by gas chromatography-mass spectral methods to be developed during the study. The nature of the hydroperoxides formed will disclose the nature of the primary oxidant, certain cholesterol hydroperoxides being formed from excited singlet oxygen, certain other hydroperoxides being formed from ground-state oxygen in radical chain reactions. A fundamental study of membrane-bound cholesterol oxidation by other common air pollutants, including ozone, nitrogen dioxide, peroxyacetyl nitrate, etc., as well as excited singlet oxygen and ground-state oxygen (for control comparisons) will be made. The thermal decompositon and enzymic alteration products of the sterol hydroperoxides will also be analyzed in order to identify the initially formed hydroperoxides with more certainty. Means of controlling or moderating cellular membrane damage from such oxidations will be sought using the fundamental analytical results obtained. Specific human tissues and cell lines most sensitive to air pollutant-moderated oxidations will be determined, and specific cause-and-effect relationships between the primary oxidative events and recognized human disorders will be sought after.